Automotive manufacturers have developed various technologies to improve fuel economy and reduce emissions in response to consumer demand and government regulations. For example, start-stop systems operate to automatically shut down and restart a vehicle's internal combustion engine to reduce the amount of time that the engine spends idling, thereby reducing fuel consumption and emissions. This is most advantageous for vehicles that spend significant amounts of time waiting at traffic lights or that frequently come to a stop while driving. Fuel economy gains from this technology are typically in the range of five to fifteen percent or more.
Vehicle start-stop systems provide various design challenges. For example, conventional starter motors are not designed for the number of operational cycles required for start-stop systems compared to conventional systems. For example, starter motors in conventional non-start-stop systems are designed to perform at least 50,000 starting cycles over a vehicle's lifetime. In contrast, starter motors in start-stop systems are designed to perform as many as 500,000-800,000 cycles over a vehicle's lifetime. Accordingly, many conventional starter motors are inadequate for the demands of start-stop systems.
In addition, vehicle accessories, such as an alternator, power steering pump, coolant pump, vacuum pump, air conditioning compressor, fan, etc., are typically driven by the crankshaft of the engine via an accessory drive (e.g., serpentine) belt. However, in start-stop systems, the accessories are not driven by the engine when the engine is shut down.